The present invention relates generally to implantable hearing aids and, more particularly, to an implantable hearing aid having one or more hermetically sealed transducers for direct coupling to the middle ear. The electroacoustic transducers of the present invention may be either a microphone or a hearing aid receiver within the implantable hearing aid of the present invention.
The implantable hearing aid is intended to help a specific class of patients for which conventional hearing aids are inadequate. These patients have severe hearing impairments and require excessive amplification. Conventional means are limited by acoustic feedback and sound distortion. Patients have reported an increased clarity of sound and were able to identify speech equal to or better than that reported with conventional aids by using amplified sound directly coupled to the middle ear bones.
An implantable hearing aid of the type discussed herein is described in U.S. Pat. No. 4,988,333 issued Jan. 29, 1991, and in a related continuation-in-part Application Ser. No. 420,292, filed Oct. 12, 1989, both of which are incorporated herein by reference. An important requirement of an implantable hearing aid is for its components to be hermetically sealed so that the environment existing inside the middle ear cavity does not corrode and/or destroy the internal parts of the hearing aid device. In the embodiment of the prior art, a transducer is acoustically connected to an acoustical coupler. The acoustical coupler has a compliant synthetic rubber diaphragm or membrane is stretched across one end of the coupler which, when the coupler is used as a microphone, may be physically attached to the handle of the malleus by a wire hook, or it may be positioned to acoustically couple with the tympanic membrane. When the coupler is to be used as a transmitter or vibrator, the diaphragm can be physically attached to the stapes or other middle ear bone via an intermediate porous ceramic wafer which is glued to the diaphragm.
However, while the synthetic rubber membranes are easily vibrated for the transmission of sound waves, it may be difficult to actually obtain the necessary hermetic seal between the diaphragm and body of the acoustic coupler. The diaphragms of the prior art devices are typically manufactured from a porous synthetic rubber material which does not provide a proper hermetic seal to adequately protect the interior of the acoustical couplers. It would be desirable to have the diaphragm manufactured from a metal or non-porous material; however, it is important that the diaphragm not lose any of its compliancy so as to be able to properly transmit the acoustical pulsations or vibrations through the acoustic coupler.
In a second embodiment of the prior art acoustical couplers, a tube having a movable piston is disclosed which is mechanically coupled either between the malleus or tympanic membrane and the transducer or between the transducer and one of the middle ear bones. However, no structure is disclosed in the prior art for providing such a hermetically sealed acoustic coupler.
Accordingly, one of the objects of the present invention is to provide a transducer for use inside the middle ear cavity having a totally hermetically sealed container without compromising the function of the transducer and acoustic coupler of the prior art devices.
It is another object to provide a hermetically sealed means for use with existing transducers to provide an implanted middle ear assistance device capable of use without significant modification of the existing transducers.